Heat sink for optical module

ABSTRACT

In one embodiment, an apparatus includes a heat sink for attachment to an optical module cage configured for receiving an optical module, a thermal interface material attached to a surface of the heat sink for thermal contact with the optical module, and a plurality of lifting elements extending from the surface of the heat sink. The lifting elements are configured to create a gap between the thermal interface material and the optical module during insertion of the optical module into the optical module cage or removal of the optical module from the optical module cage, the plurality of lifting elements positioned for insertion into aligned recesses in the optical module when the optical module is fully inserted into the optical module cage to eliminate the gap and provide contact between the optical module and the thermal interface material.

STATEMENT OF RELATED APPLICATION

The present application claims priority from U.S. ProvisionalApplication No. 63/109,000 entitled HIGH POWER QSFP-DD OPTICS COOLING

ARRANGEMENT, filed on Nov. 3, 2020, the contents of which areincorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to a heat transfer interfacebetween a heat sink and a field replaceable module, and moreparticularly, to preventing damage to the heat transfer interface duringinsertion or removal of the field replaceable module.

BACKGROUND

Due to exponential rise in bandwidth, capacity per Rack Unit (RU) hasbecome a critical parameter for system efficiency. As a result, QuadSmall Form-factor Pluggable Double Density (QSFP-DD) optical transceivermodules are getting more popular as they provide maximum capacity withina small volume. Due to the high power density of these modules, coolingof the modules is very challenging.

Cooling efficiency of optical modules may be improved by introducing athermal interface material (TIM) between a heat sink and the opticalmodule, but there is a risk of TIM damage during module online insertionand removal (OIR) in which a module is removed and replaced in the fielddue to a faulty module or to upgrade the module to a higher performancedevice.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an example of a network device with an exploded viewof an optical module cage with heat sink mounted on a printed circuitboard and optical module for insertion into the optical module cage, inaccordance with one embodiment.

FIG. 2 is a cross-sectional schematic of the components shown in FIG. 1.

FIGS. 3A-3E are schematic diagrams illustrating insertion of the opticalmodule into the optical module cage with lifting elements providing agap between a

Thermal Interface Module (TIM) on the heat sink and an upper surface ofthe optical module, in accordance with one embodiment.

FIG. 4A is a bottom perspective illustrating the TIM on a lower surfaceof a heat sink and protruding wedge elements for use in lifting the heatsink during insertion or removal of the optical module, in accordancewith one embodiment.

FIG. 4B is an enlarged partial view of the heat sink, TIM, and wedgeelements shown in FIG. 4A.

FIG. 5 is a top perspective of the optical module with grooves forreceiving the wedge elements when the optical module is fully insertedinto the optical module cage, in accordance with one embodiment.

FIGS. 6A-6D are cross-sectional views illustrating insertion of theoptical module of FIG. 5 into the optical module cage containing theheat sink shown in FIG. 4A.

FIG. 7A is a partial side view showing details of one of the wedgeelements inserted into one of the grooves with the optical module fullyinserted into the optical module cage.

FIG. 7B is a partial side view showing a direct contact thermalinterface between the optical module and TIM with the optical modulefully inserted into the optical module cage.

FIG. 8A is a top perspective of a heat sink with spring loaded ballelements for use in lifting the heat sink during insertion or removal ofthe optical module, in accordance with one embodiment.

FIG. 8B is a bottom perspective of the heat sink shown in FIG. 8A.

FIG. 9 is a partial top perspective of an optical module with dimplesfor receiving the spring loaded ball elements shown in FIG. 8B, inaccordance with one embodiment.

FIG. 10A is a perspective of the optical module of FIG. 9 inserted intoan optical module cage with the heat sink of FIG. 8A mounted on aprinted circuit board.

FIG. 10B is a cross-sectional side view of the optical module, opticalmodule cage, heat sink, and printed circuit board shown in FIG. 10A.

FIG. 10C is an enlarged cross-sectional view showing engagement of theball element with the dimple on the optical module.

FIG. 11 is a side view of a lifting element comprising a rolling ballelement, in accordance with one embodiment.

FIG. 12A is a side view of the optical module inserted into an opticalmodule cage with a heat sink containing the rolling ball elements foruse in lifting the heat sink during insertion or removal of the opticalmodule, in accordance with one embodiment.

FIG. 12B is an enlarged view of the rolling ball element seated in adimple on an upper surface of the optical module shown in FIG. 12A.

FIG. 13A is a partial side view of the assembly shown in FIG. 12A at thestart of removal of the optical module from the optical module cage.

FIG. 13B is an enlarged view of the rolling ball element shown in FIG.13A with schematics illustrating rolling direction of the ball duringremoval and insertion of the optical module.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

In one embodiment, an apparatus generally comprises a heat sink forattachment to an optical module cage configured for receiving an opticalmodule, a thermal interface material attached to a surface of the heatsink for thermal contact with the optical module, and a plurality oflifting elements extending from the surface of the heat sink. Thelifting elements are configured to create a gap between the thermalinterface material and the optical module during insertion of theoptical module into the optical module cage or removal of the opticalmodule from the optical module cage, and are positioned for insertioninto aligned recesses in the optical module when the optical module isfully inserted into the optical module cage to eliminate the gap andprovide contact between the optical module and the thermal interfacematerial.

In one or more embodiments, the heat sink comprises a pedestal and atleast one of the lifting elements is positioned along an edge of thepedestal. The remaining lifting elements extend through openings in thethermal interface material.

In one or more embodiments, the lifting elements comprise at least fourlifting elements.

In one or more embodiments, the lifting elements are offset from oneanother along a width of the heat sink.

In one or more embodiments, the recesses comprise sloped edges for easeof insertion of the lifting elements into the recesses and removal ofthe lifting elements from the recesses during insertion and removal ofthe optical module.

In one or more embodiments, at least one of the lifting elements or theoptical module comprises a coating to reduce sliding friction betweenthe lifting elements and the optical module.

In one or more embodiments the lifting elements comprise a plurality ofwedge elements and the recesses comprise grooves.

In one or more embodiments, the lifting elements comprise ball elementsand the recesses comprise dimples. In one or more embodiments, the ballelements comprise spring loaded ball elements. In one or moreembodiments, the ball elements comprise rolling ball elements. In one ormore embodiments, the ball elements are inserted into a cartridgepress-fit into the heat sink. In one or more embodiments, the ballelements are inserted into a cartridge comprising a threaded interfacewith the heat sink.

In one or more embodiments, the heat sink comprises fins extending froma side opposite the thermal interface material.

In another embodiment, a system generally comprises a heat sinkconnected to a cage, a thermal interface material extending over atleast a portion of a surface of the heat sink, a plurality of liftingelements extending from the surface of the heat sink, and a module forinsertion into the cage. The module comprises a thermal surface forcontact with the thermal interface material with the module fullyinserted into the cage and a plurality of recesses formed in the thermalsurface. The lifting elements prevent contact between the thermalinterface material and the thermal surface of the module duringinsertion of the module into the cage or removal of the module from thecage. The recesses are positioned for receiving the lifting elementswhen the module is fully inserted into the cage to provide directcontact between the thermal interface material and the thermal surfaceof the module.

In yet another embodiment, a network device generally comprises aplurality of optical module cages and a plurality of heat sinksconnected to the optical module cages, each of the heat sinks comprisinga thermal interface material on a surface of the heat sink for thermalcontact with a surface of an optical module when the optical module isfully inserted into one of the optical module cages, and a plurality oflifting elements extending from the surface of the heat sink. Thelifting elements are configured to create a gap between the thermalinterface material and the optical module during insertion of theoptical module into the optical module cage or removal of the opticalmodule from the optical module cage, and positioned for insertion intoaligned recesses in the optical module when the optical module is fullyinserted into the optical module cage to eliminate the gap and providecontact between the optical module and the thermal interface material.

Further understanding of the features and advantages of the embodimentsdescribed herein may be realized by reference to the remaining portionsof the specification and the attached drawings.

Example Embodiments

The following description is presented to enable one of ordinary skillin the art to make and use the embodiments. Descriptions of specificembodiments and applications are provided only as examples, and variousmodifications will be readily apparent to those skilled in the art. Thegeneral principles described herein may be applied to other applicationswithout departing from the scope of the embodiments.

Thus, the embodiments are not to be limited to those shown, but are tobe accorded the widest scope consistent with the principles and featuresdescribed herein. For purpose of clarity, details relating to technicalmaterial that is known in the technical fields related to theembodiments have not been described in detail.

As networking performance requirements increase, optical modules (alsoreferred to as optical transceivers, pluggable modules, or fieldreplaceable modules) continue to increase in speed and power, whilespace available to house the modules has decreased. Optical modules arethus dissipating more power in smaller form factors than conventionalcomponents. As optical power dissipation increases, cooling of opticalcomponents is becoming very difficult.

Cooling efficiency of optical modules may be improved through use of aheat sink and introduction of a thermal interface material (TIM) betweenthe heat sink and the optical module. Since metal surfaces (e.g., lowersurface of heat sink, upper surface of optical module) may have surfaceirregularities (e.g., flatness irregularities, waviness irregularities,roughness irregularities), air gaps may form between the metal surfaceof the heat sink and the optical module. These air gaps at the interfaceof the heat sink and optical module are detrimental to heat transfer dueto the low thermal conductivity of air and lead to higher thermalresistance. The TIM provides a heat transfer interface between the heatsink and optical module and may reduce or eliminate these air gaps. TheTIM thus significantly improves heat transfer for high power optics suchas QSFP-DD ZR+ or other form factor optical transceiver modules.

In conventional systems, when the optical module is inserted into anoptical module cage comprising the heat sink and TIM, the thermalinterface material engages the optical module to thermally couple themodule to the heat sink. A retention clip may be used to bias the heatsink against the optical module, thereby ensuring sufficient contactpressure at the interface when the optical module is inserted into theoptical module cage. A problem arises, however, as the optical module isinserted or removed because contact between the thermal interfacematerial and the optical module may damage the thermal interfacematerial, which may impact performance of the thermal interfacematerial, create difficulty in insertion of the optical module into theoptical module cage or removal of the optical module from the opticalmodule cage, or make equipment unusable if the damaged particles of thethermal interface material gets into the electrical connector of theequipment and impacts the electrical connection between the equipmentand the module.

The embodiments described herein provide lifting of the heat sink duringonline insertion and removal (OIR) to prevent TIM damage withoutrequiring any user intervention (i.e., passive solution). As describedin detail below, lifting of the heat sink may be provided through theuse of lifting elements, which may include a wedge profile for diecast/machined parts, circular dimples/emboss on metal sheets (as invapor chamber designs), or press-fit inserts (e.g., ball or plungerdesign). Different profiles may be used to minimize sliding resistance.Special coatings may also be used to improve sliding friction. As theoptical module is inserted into the optical module cage, the liftingelements on the heat sink provide upward movement of the heat sink toprevent TIM damage. When the optical module is fully inserted (seated),the lifting elements snap into corresponding recesses formed in athermal interface surface (e.g., top cover) of the optical module. Asdescribed below and shown in the drawings, the recesses are offset fromone another so that the lifting elements do not snap into multiplerecesses as the module slides into or out of the cage. Prevention of TIMdamage during optical module OIR provides improved thermal managementand optical module reliability. The lifting elements provide upwardmovement of the heat sink and TIM to prevent sliding contact between theoptical module and TIM to prevent TIM damage with no user intervention,thereby providing multi-source agreement (MSA) compliant solutions thatminimize cost.

The embodiments described herein may operate in the context of a datacommunications network including multiple network devices. The networkmay include any number of network devices in communication via anynumber of nodes (e.g., routers, switches, gateways, controllers, edgedevices, access devices, aggregation devices, core nodes, intermediatenodes, or other network devices), which facilitate passage of data overone or more networks. One or more of the network devices may compriseone or more optical module cages with the heat sinks described herein.The network device may include one or more processor, memory, andnetwork interfaces, with one or more of these components located on aline card removably inserted into the network device. The networkdevices may communicate over or be in communication with one or morenetworks, which may include any number or arrangement of networkcommunications devices (e.g., switches, access points, routers, or otherdevices) operable to route (switch, forward) data communications.

Referring now to the drawings, and first to FIG. 1, an example of anetwork device 10 (e.g., computing apparatus, line card) and areplaceable module 12 (e.g., optical module, optical transceiver,pluggable module, field replaceable module) that may be installed in thenetwork device is shown. The optical module 12 is inserted into anoptical module cage 14, shown mounted on a printed circuit board (PCB)15 with heat sink 18 in an exploded view in FIG. 1.

In one or more embodiments, the network device 10 comprises a pluralityof optical module cages 14 and a plurality of heat sinks 18 connected tothe optical module cages, each of the heat sinks comprising a thermalinterface material on a surface of the heat sink (shown in FIG. 2) forthermal contact with a surface 19 a of the optical module 12 when theoptical module is fully inserted (seated, properly installed) in theoptical module cage, and a plurality of lifting elements extending fromthe surface of the heat sink (shown in FIG. 2). As described in detailbelow, the lifting elements are configured to create a gap between thethermal interface material on the heat sink 18 and the optical module 12during insertion of the optical module into the optical module cage 14or removal of the optical module from the optical module cage. Thelifting elements are positioned for insertion into aligned recesses 19 bin the optical module when the optical module is fully inserted in theoptical module cage to eliminate the gap and provide contact between theoptical module and the thermal interface material.

The network device 10 includes a front surface or panel 11 with aplurality of openings (ports) 13 that provide access to optical modulecages 14 defined therein. FIG. 1 shows an exploded view of one of theoptical module cages 14 mounted on the printed circuit board 15 and theoptical module 12 that may be removably inserted into the optical modulecage. In one example, the optical module cage 14 extends from the frontpanel 11 towards a back end of a housing 16 and is positioned to besubstantially flat within the housing, such that the optical module cageis generally parallel to a cover 17 that defines of top of the housing.

It should be noted that the terms lower, upper, bottom, top, below,above, horizontal, vertical, and the like, which may be used herein arerelative terms dependent upon the orientation of the network device andcomponents and should not be interpreted in a limiting manner. Theseterms describe points of reference and do not limit the embodiments toany particular orientation or configuration.

Also, it is to be understood that the term “optical module” as usedherein refers to any modular component (e.g., optical transceivermodule, pluggable module, field replaceable module) configured forinsertion into and removal from a modular electronic system, which mayinclude a line card, stand-alone device, or any other network device.The network device 10 may comprise, for example, a line card (e.g., linecard, fabric card, route processor card, controller card, and the like),rack server, or any other network device configured to receive one ormore modules (field replaceable units). The network device 10 mayinclude any number of ports 13 for receiving any number or type ofoptical modules 12 in any arrangement.

The optical module cage 14 includes an open top that allows the heatsink 18 to access and engage the upper surface 19 a (heat transfersurface, thermal interface surface) of the optical module 12 wheninstalled in the optical module cage 14. As previously noted, aretention clip 27 may be used to bias the heat sink 18 against theoptical module 12 when the optical module is installed in the opticalmodule cage 14. With the optical module 12 inserted into the networkdevice 10, airflow enters at the front face 11 of the network device andpasses rearward over the heat sink 18 towards the inserted end of theoptical module. In the example shown in FIG. 1, the heat sink 18comprises a plurality of heat sink fins 18 a extending from a surfaceopposite the heat sink surface comprising the thermal interfacematerial. It is to be understood that the heat sink 18 shown in FIG. 1is only an example and the heat sink may include any number, shape,size, or orientation of fins in any format. In one or more embodiments,the optical module 12 may also include a heat sink 21 on the uppersurface 19 a at a front end (nose) of the optical module extending fromthe network device with the optical module fully inserted into theoptical module cage 14. In the examples described herein, the uppersurface 19 a of the optical module 12 is a heat transfer surface for theoptical module, however, it is to be understood that any surface of theoptical module may operate as a heat transfer (thermal interface)surface.

The optical module 12 may be plugged into a module based switch, router,or other optical platform port (e.g., network device 10). A cable (notshown in FIG. 1) connected to the optical module 12 at an opticalconnector may carry, for example, data (e.g., fiber optics, opticalarray, fabric). The optical transceiver module 12 operates as an enginethat bidirectionally converts optical signals to electrical signals orin general as an interface to a network element copper wire or opticalfiber. A host for the pluggable optical module may include the networkdevice 10 comprising the printed circuit board 15 and electroniccomponents and circuits operable to interface telecommunications linesin a telecommunications network. The host may be configured to performone or more operations and receive any number or type of pluggabletransceiver modules configured for transmitting and receiving signals.

The optical module 12 comprises a first end 23 a for insertion into thenetwork device 10 and a second end 23 b extending from the networkdevice when the optical module is inserted into the network device. Thefirst end 23 a of the optical module 10 defines an electrical interfaceand the second end 23 b of the optical module defines an opticalinterface between the optical module and one or more optical fibers. Thefirst end 23 a of the optical module 12 comprises an electricalconnector (back end connector) (e.g., multiple contact edge typeconnector) for electrically coupling the optical module 10 to thenetwork device (e.g., through optical module cage interface at the PCB15) and the second end 23 b of the optical module comprises one or moreoptical connectors (e.g., MPO (Multi-fibre Push On) connector or LCduplex connector). During insertion of the optical module 12 into theoptical module cage 14, the connector on the back end of the opticalmodule is coupled to a connector in the optical module cage (not shownin FIG. 1). The electrical connector may be configured to provide aSmall Computer System Interface (SCSI) connection, Serial Attached SCSI(SAS) connection, an advanced technology attachment (ATA) connection, aSerial ATA (SATA) connection, or any other suitable type of connection.

The optical module 12 may include a handle 26, which may assist withinsertion or removal of the optical module. As shown in FIG. 1, thehandle may be generally U-shaped and extend outward from a front face ofthe optical module housing. The handle 26 may also be used to operate alatch mechanism to release the optical module. During removal of theoptical module 12 from the optical module cage 14, the handle 26 (orother feature) may be used to pull the optical module from the cage. Theoptical module 12 may also be ejected or removed from the optical modulecage using any other suitable means.

The optical module may be a pluggable transceiver module in any formfactor (e.g., SFP (Small Form-Factor Pluggable), QSFP (Quad SmallForm-Factor Pluggable), QSFP-DD, CFP (C Form-Factor Pluggable), QSFP-DDZR+, CFP2, CXP (100G/Common Transceiver Pluggable), and the like) or anyother current or future standard module. In one or more embodiments, theoptical module housing may conform to industry standards packagingdimensions and may be formed from any suitable material.

It is to be understood that the network device 10, optical module 12,and optical module cage 14 shown in FIG. 1 are only examples, and otherformats, shapes, sizes, or arrangements may be used, without departingfrom the scope of the embodiments.

FIG. 2 schematically illustrates insertion of an optical module 22 intoan optical module cage 24 and a gap G between a thermal interfacematerial (TIM) 29 and an upper surface (thermal surface) 22 a of theoptical module created by a lifting system comprising a plurality oflifting elements 31 (e.g., balls, wedges, or any other shaped element)to prevent contact between the optical module and the TIM duringinsertion and removal of the optical module.

In one or more embodiments, a system comprises a heat sink 28 connectedto the optical module cage 24, a thermal interface material 29 extendingover at least a portion of a surface of the heat sink, a plurality oflifting elements 31 extending from the surface of the heat sink, and themodule 22 for insertion into the cage. The module comprises the thermalsurface 22 a for contact with the thermal interface material 29 with themodule fully inserted (seated, properly installed) in the cage 24, and aplurality of recesses 33 formed in the thermal surface. The liftingelements 31 prevent contact between the thermal interface material 29and the thermal surface 22 a of the module 22 during insertion of themodule into the cage 24 or removal of the module from the cage. Therecesses 33 are positioned for receiving the lifting elements 31 whenthe module 22 is fully inserted into the cage 24 to provide directcontact between the thermal interface material 29 and the thermalsurface 22 a of the module.

As previously described, the network device 20 includes a housing thathouses a PCB 25 and the optical module cage 24 (FIG. 2). The heat sink28 comprising the TIM 29 is coupled to the optical module cage 24. Thelifting elements 31 force the heat sink 28 and TIM 29 upward and awayfrom the upper surface 22 a of the optical module 22 to provide the gapG during insertion or removal of the optical module. The gap G allowsthe optical module 22 to be inserted into or removed from the opticalmodule cage 24 without contacting or damaging the TIM 29. As describedbelow, once the optical module 22 is fully inserted in the opticalmodule cage 24, the lifting elements are received in the corresponding(aligned) recesses 33 (e.g., grooves, dimples, openings) and the heatsink 28 automatically lowers to its seated position with the TIM 29 indirect contact with the optical module 22. As described below, therecesses 33 on the optical module 22 are offset in a directiontransverse to a longitudinal axis A of the optical module 22 along theupper surface 22 a of the optical module so that each of the liftingelements 31 only align with its corresponding groove 33 with the opticalmodule in its fully inserted position.

FIGS. 3A-3E schematically illustrate insertion of an optical module 32into an optical module cage 34 and lifting of a heat sink 38 coupled tothe optical module cage 34, in accordance with one embodiment. Aspreviously described, the optical module cage 34 includes an electricalconnector 37 a for connection to the optical module 32 and the opticalmodule comprises an optical port for receiving an optical connector 37b. As shown in FIG. 3A, the optical module 32 is aligned with an openingin the optical module cage 34. The heat sink 38 is in its lower (seated)position prior to insertion of the optical module 32 (FIG. 3A). The heatsink 38 includes a TIM 39 on its lower surface (as viewed in FIG. 3A)and lifting elements 41 (e.g., balls, wedges, plungers) extendingdownward from the lower surface. The optical module 32 comprisescorresponding recesses 43 on its upper surface (as viewed in FIG. 3A).

As the optical module 32 is inserted into the optical module cage 34(FIG. 3B) a first lifting element on a front (leading) edge of apedestal 36 of the heat sink 38 contacts the upper surface of theoptical module 32 and begins to force the heat sink upward into itslifted position. As the optical module 32 moves into the optical modulecage 34, the upper surface of the optical module contacts additionallifting elements 41, thereby forcing the heat sink 38 and attached TIM39 upwards and preventing contact between the optical module and the TIM(FIG. 3C).

As the optical module reaches its final position (FIG. 3D), the liftingelements 41 are aligned with their corresponding recesses 43 on theoptical module 32 and the heat sink 38, which may be biased downward aspreviously described, lowers to its final position with the liftingelements seated in the recesses (FIG. 3E). As previously noted, thelifting elements 41 are offset from one another along a width of theheat sink 38 so that each of the lifting elements 41 only aligns withits corresponding recess in the optical module 32 with the opticalmodule in its fully inserted position.

FIGS. 4A-4B illustrate an example of lifting elements comprising wedgeelements 40 protruding from a lower surface 42 a of a heat sink 42, inaccordance with one embodiment. As shown in FIG. 4A, a first liftingelement 40 is positioned along a front edge of a heat sink pedestal 46so that the heat sink 42 is lifted before the optical module reaches TIM49. The remaining wedge elements 40 extend through openings in the TIM49 and provide additional lift to prevent TIM damage. Any number oflifting elements 40 may be provided to create a gap between the uppersurface of the optical module and the TIM as the optical module isinserted into the optical module cage, as previously described. Each ofthe lifting elements 40 is offset from the other elements along a widthof the heat sink so that the element only falls into its finalcorresponding recess 53 (FIG. 5) on the optical module top cover(thermal surface) (FIGS. 4A and 5). As previously noted, the heat sink42 may comprise any number of heat sink fins 48 in any shape orarrangement.

FIG. 5 is a perspective of an optical module 52 comprising grooves 53for receiving the wedge elements 40 shown in FIGS. 4A and 4B. Thegrooves are offset from one another in a direction transverse tolongitudinal axis A of the optical module 52 so that the wedge elements40 do not snap into multiple grooves (recesses) 53 as the optical modulemoves longitudinally within the optical module cage (FIGS. 4A and 5).When the optical module 52 is fully inserted into the optical modulecage, the wedge elements 40 snap into the corresponding grooves 53(FIGS. 4A and 5).

In one or more embodiments, the lifting elements 40, recesses 53, uppersurface of the optical module, or any combination thereof may comprise acoating (e.g., Teflon or other coating) to reduce sliding frictionbetween the surfaces and allow for ease of insertion and removal of theoptical module 52. As shown in FIG. 5, the grooves 53 include beveledsides for ease of movement of the wedges 40 into and out of the grooves.

It is to be understood that the number of lifting elements 40 andrecesses 53 or arrangement of lifting elements and recesses may bedifferent than shown without departing from the scope of theembodiments. In the examples described herein, the optical moduleincludes four recesses corresponding to the four lifting elements on theheat sink, but there may be any number of lifting elements andcorresponding recesses in any arrangement. As previously described, afirst lifting element is preferably positioned along a leading edge ofthe heat sink pedestal so that the heat sink is lifted and the gap iscreated before the optical module comes in contact with the thermalinterface material. The location and number of the lifting elements maybe optimized based on the optical module design.

FIGS. 6A-6D illustrate insertion of the optical module 52 into anoptical module cage 64 with the heat sink 42 and TIM 49, in accordancewith one embodiment. The optical module cage 64 is mounted on a printedcircuit board 65, as previously described.

As shown in FIG. 6A, insertion of the optical module 52 begins with theright (leading) edge (as viewed in FIG. 6A) of the optical module aboutto contact the first lifting element 40 positioned on the heat sinkpedestal 46. As the optical module 52 passes the first lifting element40, the heat sink 42 lifts up, creating gap G (FIG. 6B). As the opticalmodule 52 moves into the optical module cage 64 and reaches additionallifting elements 40, the heat sink 42 has additional lift to maintainthe physical gap G and sufficient clearance with the TIM 49 (FIG. 6C).FIG. 6D shows the optical module 52 fully inserted (seated) in theoptical module cage 64. The lifting elements 40 (not shown) are seatedin the corresponding grooves on the top cover of the optical module 52.The TIM 49 is now in thermal contact with the top cover of the opticalmodule 52 to provide an efficient heat transfer interface. A reverseprocess may be performed to remove the optical module 52 from theoptical module cage 64 without damage to the TIM 49.

FIG. 7A is an enlarged partial side view showing one of the liftingelements 40 inserted into its corresponding groove 53. FIG. 7B is apartial side view showing the TIM 49 at the interface between the seatedheat sink 42 and fully inserted optical module 52 of FIG. 7A.

FIGS. 8A is a top perspective and FIG. 8B is a bottom perspective of aheat sink 82 with lifting elements comprising spring loaded balls 80. Inthis example, the wedge elements 40 of FIG. 4A are replaced with thespring loaded balls 80. As described below, the spring loaded balls 80may comprise a press-fit or threaded cartridge inserted into openings inthe heat sink 82.

FIG. 9 is a partial perspective of recesses (dimples) 93 for receivingthe spring loaded balls 80 (FIG. 8B) on an upper surface (top cover) ofoptical module 92. When the balls 80 are in a compressed position, a gapis created between the upper surface of the optical module and TIM 89attached to heat sink pedestal 86 (FIGS. 8A, 8B, and 9). When theoptical module 92 is fully inserted inside the optical module cage, thespring loaded balls 80 are aligned with the corresponding dimples 93 sothat the heat sink 82 is seated and the TIM 89 is in direct contact withthe upper surface of the optical module 92. As previously described, thedimples 93 are offset from one another to avoid the balls snapping intomultiple dimples during OIR of the optical module. The number andarrangement of the lifting elements 80 and recesses 93 shown in FIGS. 8Band 9 are only an example and other arrangements may be used.

FIG. 10A is a perspective of the optical module 92 inserted into anoptical module cage 104 with the heat sink 82 mounted on PCB 105. FIG.10B is a side view of the assembly shown in FIG. 10A. FIG. 10C ispartial cross-sectional side view illustrating details of the springloaded ball 80 seated in the recess 93 on the optical module 92. In thisexample, the spring loaded ball element 80 is contained within a pressfit housing comprising a spring 106 operable to force the ball into anextended position (inserted into the recess 93 as shown in FIG. 10C).The spring loaded ball 80 automatically depresses (spring compresses) asthe optical module 82 is inserted into or removed from the opticalmodule cage and the ball contacts the upper surface of the opticalmodule to create gap G, as shown in the cut-out view of FIG. 10C. Thespring loaded ball 80 snaps back into the corresponding recess 93 whenthe optical module 92 is fully inserted. In one example, the spring 106or ball 80 may be formed from stainless steel for operation at highertemperatures. The spring force may be optimized by adjusting the springcavity. The location and number of lifting elements 80 may be optimizedbased on heat sink dimensions, as previously noted. The spring loadedball 80 may be configured to provide minimal loading and reducedfriction. In one embodiment, a gap of 0.5-0.75 mm is maintained betweenthe TIM 89 and top cover of the optical module 92 when the balls 80 arein their compressed state (during insertion or removal of the opticalmodule). The physical gap distance between the TIM 89 and optical module92 during OIR may be customized based on the type of optical module,heat sink, and TIM implemented. It is to be understood that the liftingelement shown in FIG. 10C is only an example and other configurationsmay be used. For example, the housing may be threaded, rather thanpress-fit and other type of spring or plunger designs may be utilized.

FIG. 11 illustrates another example of a lifting element comprising arolling ball screw 110, which may be threaded or press-fit. The rollingball screw 110 allows a ball 112 to roll at its base and providesfeatures that prevent any other movement of the ball. As shown in theexample of FIG. 11, the rolling ball screw may include a stopper pin114. In this example, the ball 112 can only roll, all other movementsare restricted. Other designs may include a press-fit slotted dowel pininside the screw. The rolling ball screw 110 may be inserted into theheat sink as described above with respect to FIG. 8A using any suitabledesign and assembly process. The rolling balls 112 ensure uniform liftof the heat sink and may also reduce sliding friction, thereby improvinguser experience during OIR.

FIGS. 12A and 12B are side views of the rolling ball screw 110 with theoptical module 126 fully inserted into the optical module cage 124mounted on PCB 125. The ball element 112 is seated in its correspondinggroove 123 in the optical module 126 and the TIM 129 attached to theheat sink 122 is in direct thermal contact with the optical module.

FIGS. 13A and 13B are side views of the rolling ball screws 110 withmovement (start of insertion or removal) of the optical module. As shownin FIG. 13B, during optical module insertion (to the right as viewed inFIG. 13B), the ball rolls counterclockwise and rolls into the groove asthe screw drops down into the groove 123 with downward movement of theheatsink 122 and TIM 129. During removal of the optical module 126, theball 112 starts to roll upward out of the groove in a clockwisedirection and the screw lifts with upward movement of the heat sink 122.As the ball rolls on the upper surface of the optical module 126, therolling ball screw 110 lifts further and maintains a uniform gap betweenthe TIM 129 and the optical module thermal surface.

It is to be understood that the lifting elements in the heat sink andcorresponding recesses in the optical module shown and described hereinare only examples and other types of lifting elements and arrangement ornumber of lifting elements may be used without departing from the scopeof the embodiments.

As can be observed from the foregoing, one or more embodiments describedherein provide a cost effective solution to implement a TIM at opticalmodule and heat sink interface to improve heat transfer from high poweroptics. TIM damage is prevented during OIR of the optical module,thereby improving reliability. Any suitable TIM may be used along withany form factor optical module and the design may be compatible withstandard heat sink designs. In one or more embodiments, the retentionclip design may be optimized so that there is no significant change ininsertion or extraction forces. The location and number of liftingelements may be modified as needed for different optical module designs.The lifting elements provide a completely passive design with no userintervention needed.

Although the method and apparatus have been described in accordance withthe embodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations made without departing from thescope of the embodiments. Accordingly, it is intended that all mattercontained in the above description and shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. An apparatus comprising: a heat sink forattachment to an optical module cage configured for receiving an opticalmodule; a thermal interface material attached to a surface of the heatsink for thermal contact with the optical module; and a plurality oflifting elements extending from the surface of the heat sink; whereinsaid plurality of lifting elements are configured to create a gapbetween the thermal interface material and the optical module duringinsertion of the optical module into the optical module cage or removalof the optical module from the optical module cage, said plurality oflifting elements positioned for insertion into aligned recesses in theoptical module when the optical module is fully inserted into theoptical module cage to eliminate said gap and provide contact betweenthe optical module and the thermal interface material.
 2. The apparatusof claim 1 wherein the heat sink comprises a pedestal and at least oneof the lifting elements is positioned along an edge of the pedestal. 3.The apparatus of claim 2 wherein the remaining lifting elements extendthrough openings in the thermal interface material.
 4. The apparatus ofclaim 1 wherein said plurality of lifting elements comprise at leastfour lifting elements.
 5. The apparatus of claim 1 wherein the liftingelements are offset from one another along a width of the heat sink. 6.The apparatus of claim 1 wherein the recesses comprise sloped edges forease of insertion of the lifting elements into the recesses and removalof the lifting elements from the recesses during insertion and removalof the optical module.
 7. The apparatus of claim 1 wherein at least oneof the lifting elements or the optical module comprises a coating toreduce sliding friction between the lifting elements and the opticalmodule.
 8. The apparatus of claim 1 wherein said plurality of liftingelements comprise a plurality of wedge elements and said recessescomprise grooves.
 9. The apparatus of claim 1 wherein said plurality oflifting elements comprise ball elements and said recesses comprisedimples.
 10. The apparatus of claim 9 wherein the ball elements comprisespring loaded ball elements.
 11. The apparatus of claim 9 wherein theball elements comprise rolling ball elements.
 12. The apparatus of claim9 wherein the ball elements are inserted into a cartridge press-fit intothe heat sink.
 13. The apparatus of claim 9 wherein the ball elementsare inserted into a cartridge comprising a threaded interface with theheat sink.
 14. The apparatus of claim 1 wherein the heat sink comprisesfins extending from a side opposite the thermal interface material. 15.A system comprising: a heat sink connected to a cage; a thermalinterface material extending over at least a portion of a surface of theheat sink; a plurality of lifting elements extending from the surface ofthe heat sink; and a module for insertion into the cage, the modulecomprising a thermal surface for contact with the thermal interfacematerial with the module fully inserted into the cage and a plurality ofrecesses formed in the thermal surface; wherein said plurality oflifting elements prevent contact between the thermal interface materialand the thermal surface of the module during insertion of the moduleinto the cage or removal of the module from the cage, and wherein therecesses are positioned for receiving the lifting elements when themodule is fully inserted into the cage to provide direct contact betweenthe thermal interface material and the thermal surface of the module.16. The system of claim 15 wherein the module comprises an opticaltransceiver.
 17. The system of claim 15 further comprising a retentionclip for biasing the heat sink towards the module when the module isfully inserted into the cage.
 18. The system of claim 15 wherein saidplurality of lifting elements comprise a plurality of wedge elements andsaid recesses comprise grooves.
 19. The system of claim 15 wherein saidplurality of lifting elements comprise ball elements and said recessescomprise dimples.
 20. A network device comprising: a plurality ofoptical module cages; and a plurality of heat sinks connected to theoptical module cages, each of the heat sinks comprising a thermalinterface material on a surface of the heat sink for thermal contactwith a surface of an optical module when the optical module is fullyinserted in one of the optical module cages, and a plurality of liftingelements extending from the surface of the heat sink; wherein saidplurality of lifting elements are configured to create a gap between thethermal interface material and the optical module during insertion ofthe optical module into the optical module cage or removal of theoptical module from the optical module cage, said plurality of liftingelements positioned for insertion into aligned recesses in the opticalmodule when the optical module is fully inserted in the optical modulecage to eliminate said gap and provide contact between the opticalmodule and the thermal interface material.